Articles of manufacture are made of resin impregnated fibers cured in molds that form the skin surfaces thereof, such as poles and various cross sectional forms both of parallel and odd or tapered configuration. For example, ski poles of tapered tube form, fairings and airfoils of parallel, tapered and twisted tubular and solid form etc. Heretofore, resin impregnated fibers have been molded over and united with a core that governs configuration, the core determining shape whether or not retained within the skin formation, and whether or not a surrounding mold is employed. It is a general object of this invention, as will be described, to ensure an exacting shape to the skin of an article formed in a mold, by providing a method whereby a composite article is pressured by inherency involved in the core which can be retained or later removed as circumstances require.
The prior art methods of manufacturing sailboat masts involves, for example, the use of carbon fibers applied over an extruded aluminum mast core, with or without pressure applied but with difficulties and great expense in external application of pressure when required, for density of the resin bonded carbon filament lamina. And, said aluminum mast core is retained as the inner lamina, since the laminated mast structure requires a permanent inner form to maintain its cross sectional configuration. Likewise, the manufacture of various body and fuselage sections requires mold surfaces for establishing smooth accurately formed surfaces on the final product. For example, a body form requiring a cored wall with smooth accurately formed inner and outer surfaces requires spaced inner and outer mold forms. Further, lightweight solid or foamed cores may be required, or alternately spacing webs, ribs, stringers or spars may be required; in the structural design. Accordingly, it is an object of this invention to provide a method by which composite members fabricated of resin impregnated fibers can be pressure molded to at least one or two forms to produce smooth accurate walls of the required density. It is to be understood that pressure applied varies with the density requirement in the resin bonded filler laminate.
It is an object of this invention to provide a core that is expansible against a mold form to apply pressure to an intervening lamination while it is being cured. It is not only necessary that the mold surface be smooth and accurately formed, but that the core surface be smooth for preventing the permanent formation of imperfections such as crevices that would initiate cracks and subsequent structural failure. Accordingly, it is another object to provide a smooth surfaced or skinned core that produces a commensurately smooth inner wall. It is still another object to provide heat means compatible with the curing of resins and which simultaneously causes the expansion and pressure application by said core. With the present invention, gas filled noninterconnected cellular core material is employed, supplemented by structural means to increase pressure when required.
A feature of this method is the controlled internal expansion within the core, and its applicability to most all molding situations. The mold can be planar with or without curvatures and/or detail, the mold can be tubular and the core retained or removed, the mold can be comprised of inner and outer forms between which a cored wall is molded; examples of which are shown and hereinafter described.